1. Field of the Invention
The present invention relates to grippers and more particularly a gripper having dual pneumatic actuators design to hold delicate parts.
2. Description of Prior Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
A gripper assembly is a mechanical device used to hold or clamp a workpiece. Grippers are used in many different applications in which a workpiece must be machined, assembled with other parts, tested, packaged, transported or handled in some manner. Grippers often include opposing jaw members or similar parts which can be moved along one or more guides on the surface of a base.
The jaw members are moved toward and away from each other. The jaw members are moved toward each other to hold a workpiece in a secure manner such that it can be worked on. The jaw members are moved away from each other to release the workpiece after work on the workpiece has been completed.
The jaw members may be moved by a variety of different type actuators which are mechanically coupled to the jaw members. The actuators can be electrically driven, such as a motor. The actuators can also be fluid driven, for example a hydraulic or pneumatic cylinder with an internal piston. The actuators can be coupled to the jaw members using various types of mechanical linkages, depending upon the type of actuator. Electrically driven actuators can be coupled to the jaw members by rack and pinion type assemblies. Fluid driven actuators can be connected to the jaw members by linkage elements, by a flexible filament, cable or rope.
Some grippers use a single actuator, such as a reversible motor to move the jaw members toward or away from each other. Other grippers use a fluid driven actuator and a spring combination where the spring is compressed as the jaw members are moved in one direction as the actuator is energized and the spring causes the jaw members to move in the reverse direction when the actuator is de-energized. Also known is the use of opposing fluid driven actuators to move the jaw members independently at different speeds and/or under different forces if the fluid driven actuators are not properly balanced.
The selection of a particular type of actuator and of the configuration of the mechanical link coupling the actuator to the jaw member determines the characteristics of the gripper assembly and is often dictated by the particular type of workpiece that the gripper assembly is designed to be used with and the particular kinds of operations being performed on the workpiece as it is clamped in the gripper assembly.
In cases where it is desired to have the jaw members close at the same speed and/or exert the same amount of force, a synchronizing mechanism may be incorporated into the linkage between the actuator and the jaw member. The configuration of the synchronizing mechanism depends upon the type of actuator selected and the result that the gripper assembly is designed to achieve.
For example, U.S. Pat. No. 8,905,452 issued Dec. 9, 2014 to Williams discloses a rack and pinion linkage as a force-multiplying mechanism to connect an electric motor to the jaw members. U.S. Pat. No. 6,598,918 issued Jul. 29, 2003 to Null discloses a gripper with a synchronizing mechanism which controls the speed of the jaw members as well as the force applied by the jaw members.
However, one of the problems inherent in conventional gripper assemblies is that they cannot be used effectively to retain delicate workpieces such as computer chips and fragile parts made of glass. This is in large part because friction prevents conventional grippers from being controlled precisely enough to apply very low force to the workpiece and at the same time clamp the workpiece firmly enough to prevent movement of the workpiece as it is being worked on.